Structure Of Phosphors Research Articles

Geometrical and Electronic Structures of Red Phosphors Doped with 3d Transition Metals

Phosphors have become increasingly important in our lives with the spread of white LEDs in recent years. The most basic structure of a white LED is a combination of a blue LED and a yellow phosphor, but this combination results in a white color with a high color temperature that leans toward bluish-white. Therefore, red and green phosphors are demanding in order to adjust the color temperature and improve color rendering property. In addition to the demands of high efficiency and long-term stability for such phosphors, it is also important that the raw materials are low-priced. Many red phosphors achieve red fluorescence by adding a few percent or less concentration of rare earth elements. However, their supply may become unstable, since rare earth elements are unevenly distributed in certain regions of the earth. Therefore, it is requested that the phosphors without rare-earth elements. Recently we have reported stable rare-earth free res phosphors using 3d transition metals with 3d3 configuration, such as Cr3+ and Mn4+, to replace rare-earth elements [1-3]. In the current study, geometrical and electronic structures of phosphor materials doped with Cr3+ and Mn4+ are demonstrated both experimentally and theoretically. Especially, we focus upon the local environment of doped 3d transition element, which are studied in detail by X-ray absorption near edge structure (XANES) and electron spin resonance (ESR) analysis with the aid of the first-principles calculations.

Evaluation of luminescent and thermal properties of Dy³⁺ doped tungstate phosphors for optoelectronic and thermometry applications

Novel Ca2MgWO6: xDy3+ (x = 1, 2, 3, 4, and 6 mol%) phosphors were synthesized via solid-state reaction method. The phosphor structure remained unchanged upon doping with Dy3+ ions. Phosphors were optical optimizated using 4F9/2 → 6H13/2 transition, and 3 mol% of Dy3+ was found to be optimal concentration. We investigated optical quenching mechanisms including energy transfer, cross-relaxation, charge compensation, and multipole-multipole interactions. Colorimetric analyses assessed colour coordinates, purity, and correlated colour temperature (CCT). The optimized phosphor showed a direct band gap of 3.68 eV, a refractive index of 2.24, and covalent bonding between Dy3+ and the host. It exhibited exceptional thermal stability with only 0.31 wt% loss up to 440 °C. Temperature-dependent emission spectra indicated high optical quenching temperature (498.82 K) and activation energy (0.21 eV). A multi-transition ratiometric approach confirmed suitability for non-contact thermometry and LED applications.

Design of a PIT biosensor based on plasmonic-graphene-black phosphorous hybrid for hypercholesterolemia detection

Cardiovascular diseases are the primary and fundamental reasons of people death around the world. Precise, fast responding, compact and integrable biosensors are considered as the most important prevention or treatment devices. In this work, remarkable absorbers based on graphene-plasmonic-black phosphorous hybrid structures are proposed. These devices are utilized for bio-sensing applications. The presented device is consisted of different quarter-cylindrical and plate shaped layers of graphene, black phosphorous, Ag, Au and Al2O3. In order to improve functionality of the presented absorber (improving the absorption’s peak value), effects of structural parameters and chemical potential (Ef) on the absorption spectrum are being considered. The proposed structure will be considered as a biosensor for detection of cholesterol concentrations in blood samples (this would help physicians in diagnosis of hypercholesterolemia and prevention of cardiovascular diseases), after improving its characteristics. Finally, it is expected for this biosensor the following remarkable sensitivity, figure of merit, quality factor and detection limit of 6045.6 nm/RIU, 237.61 RIU− 1, (80.3–90.1) and (2.1e-4–2.26e-5) RIU, respectively. Therefore, the proposed device can be an appropriate candidate for bio-sensing applications in optical integrated circuits.

High thermally stable and efficient rare-earth celsian by phase transformation of Ba2+-Exchanged SOD zeolite

The white LEDs with high performance and excellent luminous quality is of high importance for developing the current lighting industry, and high thermally stable blue phosphors play a critical role in the preparation of white LEDs. Herein, we reported a facile way to obtain highly efficient blue Eu2+-doped celsian phosphor with excellent thermal stability by a phase transformation of Ba2+-exchanged SOD Zeolite strategy. The structure of phosphors changed from nepheline to celsian with the doping of Ba2+, and the maximum emission intensity blue-shifts from 550 nm to 450 nm under the excitation of 370 nm. The PLQY is determined to be 56 %, 96 % and 82 % for the phosphor with Ba2+ doping concentration being 0, 1.49 and 1.86, respectively, and the luminescence intensity at 423 K is can be 80 %, 102 % and 93 % of its intensity at room temperature. Finally, the package of the LED device based on our yellow and blue phosphors together with the commercial red CaAlSiN3:Eu2+ phosphor is constructed to show warm white light with the CCT of 3705 K and a high CRI of 97.7. This study provides a facile way for obtaining satisfactory phosphors for high-quality lighting.

Synthesis, Structure and Luminescence Properties of Mn-doped MgAl2O4 Red-Emitting Phosphors with Varying Sintering Temperature.

Oxide matrix red-emitting phosphors are deemed as excellent color converters for white light emitting diodes (WLEDs) and laser diodes (LDs). Manganese-doped MgAl2O4 powder was synthesized by a solid-state reaction method at different sintering temperatures. Microstructure shows that grain size is mainly in the range of 0.2-5μm, and grain agglomeration occurs with increased sintering temperature. XPS analysis indicates that the doped Mn ion exhibits a valence state of + 4 within the MgAl2O4 matrix. The diffraction peak of the phosphors is shifted by the sintering temperature, which affects lattice constant. Upon excitation by 300nm ultraviolet light, the samples emit asymmetric broadband red light within the range of 620-720nm, attributed to Mn4+ ion's transition from 2Eg to 4A2g states. With the increasing temperature, the main emission peak shifts from 677nm to 650nm, ascribed to the change in energy level (2Eg) resulting from the reduction of Al2O3 phase. Crystal field theory confirmed that Mn4+ ions are within a strong crystal field environment created by MgAl2O4 matrix. By affecting particle size and crystallinity, the sintering temperature influences the fluorescence lifetime of the Mn4+ ion. Notably, these red-emitting phosphors exhibits remarkable thermal stability as their emission intensity remains approximately at 58% of initial intensity even at elevated temperature (435K). Consequently, Mn4+: MgAl2O4 red-emitting phosphors with high thermal stability render them promising candidates for WLED applications.

Investigation of red-emitting CaMoO4: Eu3+ phosphor by partitioning of substitutional PO4 3- ions via solid-state reaction method.

To investigate the impact of PO4 3- anionic groups, the trivalent europium ion-doped calcium molybdate (CaMoO3-PO4:xEu3+, where x = 0.5, 1.0, 1.5, 2.0, and 2.5mol%) phosphors were synthesized using the solid-state reaction method. The detailed study of the phosphor materials was carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), optical diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The XRD results indicate that the substitution of PO4 3- anion and Eu3+ dopant ion did not affect the crystal structures of the CaMoO4 phosphors. Ultraviolet-visible (UV-vis) absorption analysis revealed the change of absorption edge of both un-doped and Eu3+-doped CaMoO4-PO4 phosphors. Under the 394 nm UV-excitation, the recorded PL spectra showed an intense peak at 615 nm corresponding to the Eu3+: 5D0 → 7F2 transition. The results of the Commission Internationale de l'Eclairage (CIE) diagram reported that the color of the emissions lies in the red color zone and there is no change in the CIE coordinates of the overall emission for Eu3+-doped CaMoO4-PO4 as Eu concentration changes. Thus, these observations led to finding the best red components for white light-emitting diode applications.

Enhancement of upconversion luminescence and temperature sensing performance in Er3+/Yb3+ doped Lu2O3 and Lu2O2S phosphors by incorporation of lithium ions

A series of spherical Er3+/Yb3+ doped Lu2O3 and Lu2O2S phosphors co-doping with varying concentrations of Li+ (0, 1, 3, 5, and 7 mol%) were synthesized by homogeneous precipitation method followed by direct calcination or sulfurization. The crystal structure and morphology of the as-prepared phosphors were characterized by XRD, FTIR and SEM. Meanwhile, the upconversion (UC) luminescence spectra were recorded under 980 nm laser excitation at temperatures ranging from 303 to 573 K. The incorporation of lithium ions led to an enhancement of UC luminescence intensity by about 15 times at room temperature. The introduction of Li+ could also affect the temperature sensitivity of the samples. Furthermore, optical temperature sensing of the phosphors was achieved by analyzing the fluorescence intensity ratio (FIR) of thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs). Impressively, utilizing the non-TCLs approach resulted in maximum Sa values of 8.80 %K−1 and 11.06 %K−1 for the Er3+/Yb3+/5 % Li+ doped Lu2O3 and Lu2O2S phosphors, leading to an approximately 17-fold and 23-fold increase compared to that of TCLs-based approach, respectively. The results of this work demonstrate the great potential of Er3+/Yb3+/Li+ doped Lu2O3 and Lu2O2S phosphors for optical thermometers.

A Lu3Sc2Ga3O12: Eu3+ red-emitting phosphor with excellent optical properties and thermal stability was obtained by partially replacing Lu3+ with Gd3+ / Y3+

A novel red phosphor Lu3(1-x)Sc2Ga3O12: xEu3+(0 ≤ x ≤ 0.3) was successfully prepared by high temperature solid state method. The Lu2.4Sc2Ga3O12: 0.2Eu3+ phosphor shows strong high internal quantum efficiency and thermal stability with values of 64.79 % and 87.0 %, respectively. Based on Lu2.4Sc2Ga3O12: 0.2Eu3+ phosphor, the partial replacement of Lu3+ ions in the host by Gd3+ / Y3+ ions changes the local crystal field environment of Eu3+ ions, resulting in wonderful changes in the luminous center, and the luminous intensity at 593 nm is increased by 3.66 and 3.54 times, respectively. The decay time of Eu3+ ions is analyzed from the perspective of dynamics, and the reasons for the enhancement of luminescence after partial replacement of Lu3+ ions are discussed in detail from two aspects of phosphor structure and crystal field effect around Eu3+ ions. In addition, with the substitution of Gd3+ / Y3+ ions, the thermal stability of the sample is 90.3 %/89.4 % with excellent low thermal quenching. The thermal quenching mechanism is described by combining Debye temperature and activation energy. The sample also has a high internal quantum efficiency IQE=79.03 % / 78.24 %. Finally, under the excitation of 365 nm chip, the phosphors of Lu2.34Sc2Ga3O12: 0.2Eu3+, 0.02Gd3+ and Lu2.34Sc2Ga3O12: 0.2Eu3+, 0.02Y3+ synthesized R-LED device has extremely high color rendering index, Ra is 78.23/77.15 and color temperature is 1640.38 K/1642.97 K. The experimental results show that the Lu2.34Sc2Ga3O12: 0.2Eu3+, 0.02Gd3+ / Y3+ phosphors prepared has a wide application prospect in w-LED devices.

Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors for plant growth lighting and temperature sensor

Novel Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors were synthesized using a high-temperature solid-phase method. The crystal structure and luminescence properties of phosphors were systematically investigated by experimental characterization and theoretical calculation. Under excitation at 375 nm, Y2MgTiO6:Bi3+, Mn4+ phosphors exhibit two emission bands located at 410 nm and 696 nm (blue and red), which can well be matched with the absorption bands of chlorophylls a, b and phytochrome. The Y2MgTiO6: Bi3+, Mn4+ luminescence remains at 66.2 % intensity at 423 K and quantum yield is 52.06 %. Optical temperature properties of Y2MgTiO6:Bi3+, Mn4+ were investigated using fluorescence intensity ratio (FIR) analysis and were found to reach a maximum relative sensitivity of 2.93 % K−1 at 498 K. The study suggests that this material could be a potential option for indoor plant culture and optical temperature sensing.

Temperature- and pressure-dependent luminescence properties of K3AlF6: Cr3+ phosphor

Temperature and pressure are two effective methods to tune the structure and luminescence properties of phosphors. In this study, tetragonal K3AlF6: Cr3+ phosphors were synthesized through the solid-state method. Its structure stability and luminescence property were in situ studied under temperature and pressure using differential scanning calorimetry (DSC), Raman, and photoluminescence spectra. At ambient conditions, one broadband emission presented in the 1.3–1.9 eV range due to the 4T2→4A2 transition. Three phase transitions presented with increasing temperature to 400 °C, but no much change was observed for its luminescence property. In contrast, its structure was stable during compression, and no phase transition was observed up to 26.1 GPa. Furthermore, the crystal field around Cr3+ was enhanced under pressure, leading to its luminescence changing from broad 4T2→4A2 emission to narrow 2E→4A2 emission above 4.2 GPa. It was suggested that pressure was more effective for K3AlF6:5%Cr3+ phosphor. This result provides one effective method to modulate the luminescence property of Cr3+.

Effect of Tb3+ and Ce3+ Co-doping on the Structure and Photoluminescence Properties of Hexagonal Boron Nitride Phosphors.

In the paper, we have successfully prepared hexagonal boron nitride (h-BN:Tb3+, Ce3+) phosphors with melamine as the nitrogen source. The X-ray powder diffraction patterns confirm that the sample possesses a hexagonal crystal structure within the P m2 space group. It is interesting that the co-doping combination of Tb3+ and Ce3+ can markedly enhance the threshold concentration of doped activators within the limited solid solution of h-BN phosphors. Under 302nm excitation, the h-BN:Ce3+ phosphors exhibit broadband blue light emission at 406nm. In h-BN:Tb3+, Ce3+ phosphors, the co-doping of Ce3+ not only ensures high phase purity but also results in strong green light emission. The energy transfer efficiency from Ce3+ to Tb3+ is about 55%. The fluorescence lifetime increases with the increase of Ce3+ and Tb3+ concentration, and the fluorescence lifetime of h-BN:0.025Tb3+, 0.05Ce3+ phosphor reached 2.087ms. Additionally, the h-BN:0.025Tb3+, 0.05Ce3+ phosphor exhibits excellent thermal performance with an activation energy value of 0.2825eV. Moreover, the photoluminescence quantum yield of the sample exceeds 52%. Therefore, the h-BN:Tb3+, Ce3+ samples can be used as green phosphors for solid state lighting and fluorescent labeling.

Energy transfer from Ce3+ to Eu3+ in the spinel structure of ZnAl2O4 phosphor for optoelectronic applications

Zinc aluminate (ZnAl2O4), with a spinel structure is known for its versatile applications as catalyst, ceramic material, and optoelectronic device. ZnAl2O4 is an excellent host for trivalent rare-earth ions such as Dy3+ , Tb3+, Eu3+ and Sm3+ has been extensively investigated for application in display devices. The focus of this work is on Ce3+ and Eu3+ co-dopants aiming to address issues such as multistage combustion synthesis routes, the formation of secondary phases, that often impact luminescence intensity. Through a systematic approach, we synthesized the ZnAl2O4 host with consistent cerium concentration and varying europium ions using one-step combustion synthesis route. The findings reveal that the synthesized material exhibits efficient energy transfer, mitigates concentration quenching and demonstrates favorable color chromaticity. The crystal structure analysis confirms phase purity and addresses concerns related to secondary phase formation. The simplified and cost-effective approach of one-step combustion synthesis method for synthesizing Ce3+ and Eu3+ co-doped ZnAl2O4 suggests that this phosphor has potential applications in ultraviolet photo-electronic technology and other opto-electronic devices.

CaO:Tb<sup>3+ </sup> green-emitting phosphor for white light-emitted diode-phosphor applications: the improvement of light output intensity

The use of CaO:Tb3+ with light green emission on for improvement of both luminescent output and chromatic fidelity of the white light emitted from a light-emitting diode (LED). The CaO:Tb3+ is combined with the yellow-emitting phosphor of YAG:Ce3+ to provide sufficient colored spectral proportion for the white light generation, enhancing the color performance. The phosphor combination is utilized for the three most applied LED structures: conformal, in-cup, and remote phosphor structures. The changes in optical properties of these three LEDs are monitored with adjustments in the proportion of CaO:Tb3+. The higher proportion of the green phosphor results in higher scattering efficiency in all structures, offering better color coordination and stronger luminous flux. The color quality scale is somehow reduced when CaO:Tb3+ concentration is more than a certain level. Therefore, depending on the phosphor configuration of the white light-emitting diode (WLED), the concentration of CaO:Tb3+ should be modified to achieve a good color rendition with improved color consistency and luminous properties.

Characterization of Sm3+-activated carbonated calcium chlorapatite phosphors for theranostic applications: a comparative study of co-precipitation and hydrothermal methods.

Continuous efforts are ongoing to discover new luminescent materials with appropriate properties for applications in medicine, serving as theranostic agents for healing and bioimaging. In this paper, novel single-phase carbonated calcium chlorapatite (Ca10(PO4)5(CO3)Cl2, abbreviated as CaClAp-CO3) phosphors activated with varying concentrations of Sm3+ ions were successfully fabricated using both co-precipitation and hydrothermal methods to investigate the influence of the synthesis techniques on the physicochemical properties of these materials. The effects of doping concentration of Sm3+ ions and synthesis techniques on the structure, photoluminescence (PL), energy transfer, substitute sites, fluorescence lifetime and luminescence colour of phosphors were investigated. The synthesized phosphors were characterized by X-ray diffraction (XRD) to confirm their crystal phase structure and purity. Vibrational features and the incorporation of carbonate ions were verified using Fourier-transform infrared (FTIR) spectroscopy. The obtained materials emit reddish-orange light, primarily from the most intense 4G5/2 → 6H7/2 transition. The electric dipole to magnetic dipole transition ratio (ED/MD), CIE colour coordinates and colour purity were determined to provide additional insights into the spectroscopic attributes of the obtained phosphors. In addition, the concentration quenching was also observed, and its mechanism was proposed based on theoretical calculations showing the multipolar interactions.

Structure and luminescence characteristics of self-activated vanadate garnet phosphors.

Vanadate phosphors include [VO4] tetrahedra with Td symmetry. Due to the charge transfer (CT) between V5+-O2-, the phosphor with [VO4] tetrahedra exhibits strong emission in the visible region and can effectively absorb ultraviolet (UV) light. Garnet structured vanadate phosphors have attracted much attention due to their easily controllable composition. In this paper, we successfully prepared phosphors with high quantum efficiency. The lattice structure and luminescent properties of the samples were studied in detail. Vanadate garnet phosphors have the same structure. The phosphors exhibit broadband emission peaks under 266 nm and 355 nm near-ultraviolet (UV) excitation, emitting bright greenish-white and yellowish-white light. The emission wavelength of the phosphor is red-shifted. The phosphors exhibit high internal quantum efficiency (IQE) for the NaSr2Mg2V3O12 and KCa2Mg2V3O12 samples. In this paper, the structure and luminescence characteristics of greenish-white-emitting and yellowish-white-emitting vanadate phosphors with high quantum efficiency are investigated.

Synthesis of Bi3+ and Eu3+ co-doped Na4CaSi3O9 blue-red light tunable emission phosphors for inducing plant growth

Sunlight is an important factor in plant growth. In this regard, both blue and red lights provide significant contributions. Blue–red light dual-emission phosphors, which can be achieved by regulating energy transfer between two independent luminous centers, have recently been investigated extensively. In this study, Bi3+ and Eu3+ co-doped Na4CaSi3O9 (NCSO: Bi3+, Eu3+) phosphors are successfully synthesized via a high-temperature solid-phase method at approximately 900 °C for a few hours. X-ray powder diffraction is used to verify the crystal structure, phase purity, and structural refinement of the NCSO-based phosphors. Upon light excitation at 299 nm, the phosphors show blue–red dual emission. The blue emission (300–500 nm) may have originated from the 3P1 → 1S0 transition of Bi3+, whereas the red emission (575–725 nm) is attributable to the 5D0 → 7FJ (J = 1, 2, 3 and 4) transition of Eu3+ ions. Energy transfer from Bi3+ to Eu3+ is systematically investigated and the thermal stability of the phosphors is analyzed using temperature-dependent spectroscopy. The emission spectra of NCSO: Bi3+, Eu3+ are consistent with the absorption spectra of chlorophyll a, chlorophyll b, phytochrome PR, and phytochrome PFR. These results indicate that the obtained phosphors exhibit significant potential for inducing plant growth.

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor

Effect of synthesis temperature on crystal structure, optical and magnetic properties of SmCuO3-δ ceramic phosphor is investigated in this work. The SmCuO3-δ ceramic has been synthesized using a sol-gel method. Rietveld analysis reveals that SmCuO3-δ ceramic crystallizes into coexisting tetragonal (I4/mmm) and monoclinic (C2/c) crystal structures. The phase fraction of the tetragonal and monoclinic phases strongly depends on the synthesis temperature. The crystallite size and particle size increase with increasing calcination temperature. The X-ray photoelectron spectroscopic spectra reveal the presence of (Cu2+, Cu3+) and (Sm2+, Sm3+) ions alongwith the oxygen vacancy centres in the phosphor. The SmCuO3-δ ceramic shows multiple magnetic phase transitions. The FTIR spectra show the presence of vibrational bands due to Cu-O and Sm-O groups. The optical band gap of the SmCuO3-δ phosphor decreases with an increase in calcination temperature and crystallite size. The photoluminescence excitation spectra show the peaks at 363, 402, 505 and 542 nm at the fixed emission wavelength of 609 nm, whereas the photoluminescence emission spectra contain peaks at 465, 515 and 609 nm at the fixed excitation wavelength of 402 nm. The photoluminescence emission intensity of the sample increases with the rising calcination temperature upto 900 °C and finally, it quenches at 1000 °C. Therefore, the SmCuO3-δ ceramic phosphor may be useful for solid state lighting, LEDs and magnetic devices.

The use of CaO:Eu<sup>3+</sup> and Zn<sub>2</sub>SiO<sub>4</sub>:Mn<sup>2+</sup> phosphors to increase the color quality and illumination intensity of WLEDs

The lumen efficacy in remote phosphor structure displayed remarkable enhancements, which is notable for the development of white light-emitting diodes (WLEDs). Nevertheless, its quality of colour is deemed not as good as that of the conformal or in-cup phosphor structure. Therefore, the goal of this research is to achieve a better quality of colour and significant luminous flux value for remote phosphor configuration by using extra phosphor layers. In particular, the two-layer and three-layer structures with the implementation of green and red phosphors are proposed. Comparing these two structures can help pinpoint the best suited for the WLED production. The assessment of each structure’s effect on the WLEDs’ optical parameters was determined under various correlated temperatures of colour (5,600-8,500 K). The outcomes indicated that the three-layer structure enhanced the quality of colour with greater efficiency compared to the two-layer structure due to the increased color rendering index (CRI), color quality scale (CQS), and photoluminescence (PL), and reduced colour deviation. The scattering improvement of the three-layer structure is a key factor of these accomplishments, proven by the scattering theory of Mie. Therefore, the three-layer structure is potential for developing WLED production.

Luminescent Properties of (Ca7ZrAl6O18-Ca3Al2O6-CaZrO3):Eu3+ Composite Ceramics and Tracing in the Hydration Process

In this work, solid-state reaction sintering was used to fabricate Ca7ZrAl6O18-Ca3Al2O6-CaZrO3:Eu3+ ternary composite ceramics and cements. The structural, microstructural, and spectroscopic properties of the ceramics with different Eu2O3 content were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and spectrofluorimetry, respectively. The XRD patterns analyzed with Rietveld refinement confirm the presence of the orthorhombic phase of Ca7ZrAl6O18 and the cubic phase of Ca3Al2O6 in all the samples, indicating that doping of Eu3+ slightly changes the crystalline structure of both aluminate phosphors. EDS analysis revealed that the Eu doping element was strongly concentrated to the two phases, i.e., Ca7ZrAl6O18 and Ca3Al2O6, with the Eu concentrations of 8.45 wt.% and 8.26 wt.%, respectively. The luminescent properties of the ceramics doped with different Eu3+ ion concentrations were investigated by excitation and emission spectroscopy at room temperature. These results were compiled using a laser with an optical parametric oscillator (OPO) system. The obtained spectra indicated changes in the luminescence intensity and shape occurring with phase composition and Eu2O3 concentration. The emission spectra of the ceramics exhibit a strong dependence on the excitation wavelength in the range from 210 to 300 nm, and invariably, five peaks were assigned to the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+. The luminescence spectroscopy was then used to trace the early and long-term hydration behavior of cements. Thus, luminescence spectroscopy may provide a new tool for non-destructive testing of cement-based structures.

Unique sandwich and microstructure design of phosphor-in-glass film for high brightness laser-driven white lighting

All-inorganic phosphor-in-glass (PiG) converter withstanding high power laser excitation has garnered attention for laser-driven white lighting, while its poor heat dissipation and low fluorescence conversion efficiency has been serious challenges in high-brightness white lighting. Herein, a thermally robust PiG film converter with a sandwich phosphor structure and microstructure interface was designed for ultrahigh-brightness laser-driven white lighting. The yellow-emitting YAG PiG film was thermocompression bonded to microstructure sapphire (MS) and planar alumina (PA) to construct the MS-PiG-PA converter. The YAG PiG film possess higher luminescence intensity than YAG phosphor and was tightly attached to sapphire and alumina without microcracks. Benefiting from the double-sided heat dissipation design and microstructure interface light field strengthening effect, the MS-PiG-PA converter emits ultrahigh luminous flux white light (5197 lm) at power density of 30 W/mm2 and displays excellent CRI and CCT stability. The MS-PiG-PA converter has a lower working temperature, higher saturation threshold and luminous efficacy.